The present invention relates to a uniflow regenerative shaft furnace for calcining limestone and similar mineral raw materials utilizing liquid fuels introduced by means of fuel lances suspended in the bulk material at the preheating zone of the furnace. The shaft furnace includes at least two shafts connected in flow communication through a transfer duct with the shafts being alternately operated one as the calcining or uniflow shaft and the other as the counterflow shaft.
A regenerative process for calcining mineral raw materials known from Austrian AT-PS 211,214 is frequently used for the construction of uniflow/counterflow shaft furnaces having at least two shafts. In uniflow regenerative shaft furnaces having at least two shafts, it is known to use gaseous and liquid fuels; see, for example, the magazine "Zement-Kalk-Gips" (cement-lime-Gypsum), no. 6, 1970, pages 217ff.
When furnaces utilizing this system were initially constructed, swivel burners were selected for supplying the liquid fuels. These swivel burners spray oil at a transition between a preheating zone and a calcining zone of the furnace beneath a burner bridge directly onto the bulk material to be calcined arranged in this location. Due to the fact that temperatures in the range of about 700.degree. Celsius prevail at this location, the oil is vaporized very rapidly and it subsequently burns with combustion air which flows downwardly in the uniflow shaft of the furnace.
For furnaces utilizing this system which were heated by gas, for example, natural gas, vaporized liquified gas or light gasoline, coke-oven gas, mixed gas, etc, fuel lances made of steel tubes were used from the beginning, wherein the lances were directly suspended in the limestone bulk material of the preheating zone. For vaporized liquidified gases, insulated steel tubes have also been found suitable.
If it is attempted to use fuel lances which are suspended in the bulk material for the supply of liquid fuels, significant difficulties become unavoidable. Due to the temperatures prevailing in the fuel lances, cracking or coking of the oil occurrs which subsequently results in clogging of the fuel supply tube.
The present invention is directed toward development of a fuel lance structure for furnaces of the type described whereby use of liquid fuels is possible without creating problems in the preheating zone of the calcining shaft of the furnace.